LU-16285 ldlm: BL_AST lock cancel still can be batched

LU-16285 ldlm: BL_AST lock cancel still can be batched

The previous patch makes BLAST locks to be cancelled separately.
However the main problem is flushing the data under the other batched
locks, thus still possible to batch it with those with no data.
Could be optimized for not yet CANCELLING locks only, otherwise it is
already in the l_bl_ast list.

Lustre-change: https://review.whamcloud.com/50158
Lustre-commit: 9d79f92076b6a9ca735dbe4420c122f47d240263

Fixes: b65374d9 ("LU-16285 ldlm: send the cancel RPC asap")
Signed-off-by: Vitaly Fertman <vitaly.fertman@hpe.com>
Signed-off-by: Xing Huang <hxing@ddn.com>
Change-Id: Ie4a7c7f3e0f5462290f72af7c3b2ff410a31f5e7
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/50274
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>